arXiv subjects

Nikolaus Z. Prusinski

Publications and source records attributed to Nikolaus Z. Prusinski.

14 recordsLinked to original sources

arXiv2026

KBSS-InCLOSE II: First Detailed Insights on the Inner CGM of Low-Mass $z\sim2.3$ Galaxies

We present results from an extension to the Keck Baryonic Structure Survey (KBSS) that focuses on the Inner Circumgalactic Medium (CGM) of QSO Line Of Sight Emitting galaxies at z$\sim$2.3 (InCLOSE). We analyze two low-mass galaxies $\log{(\rm{M_*} / \rm{M_\odot})} \leq 9$ that are within small a projected distance of a QSO $D_{\rm tran} \leq 50~{\rm kpc}$ ($D_{\rm tran} /R_{\rm vir} \leq 0.75$). One galaxy is detected as a bright Lyman- Emitter with Keck/KCWI (confirmed with follow-up Keck/MOSFIRE spectra), and the other as a serendipitous line emitter with Keck/MOSFIRE. Both galaxies have nebular and morphological properties consistent with those of typical low-mass z$\sim$2.3 star-forming galaxies. Analysis of their CGM absorption as seen with Keck/HIRES spectra of the background QSOs shows no detections of low-ionization metal absorption (low-ions; e.g., Si II), ubiquitous detections of intermediate- (e.g., C IV) and high-ions (O VI), kinematically complex absorption ($\geq$7 components per galaxy halo) spread over $|Δv|\pm 150~{\rm km~s^{-1}}$, and no unambiguously unbound gas is detected in either galaxy halo. We analyze the thermal properties of a subset of CGM components, finding that the majority (6/10) have temperatures consistent with heating from the metagalactic UV background ($\log{(T/\rm{K})_{\mathrm{med}}}=4.0$) while the remainder possess short-lived, intermediate temperature gas that would require additional heating or rapid replenishment ($4.6 \leq \log{(T/\rm{K})} \leq 5.1$), the internal energy of these absorbers are dominated by thermal broadening, their internal (turbulent) velocities are all subsonic, while their motions through the halo are likely supersonic. These results hint that the z2.3 CGM changes with stellar mass in terms of kinematic complexity and unbound gas fraction, while thermal properties remain similar.

astro-ph.GA↗

arXiv2026

Follow-up of SN 2025wny II: Superluminous Supernova Physics at Cosmic Noon

SN 2025wny is a gravitationally lensed, hydrogen-poor superluminous supernova (SLSN-I) at z = 2.015. To date, it is the most extensively observed high-redshift core-collapse SN and has the most detailed rest-frame UV observations of any SLSN. We present densely sampled rest-frame UV-to-optical photometry and spectroscopy out to +80 d post-peak (rest frame) from several facilities, including JWST, Keck, VLT, Gemini, the Palomar 200-inch, the Fraunhofer Telescope at Wendelstein, and the Liverpool Telescope. Correcting for lensing magnification, SN 2025wny reaches a peak pseudo-bolometric luminosity of $L_{\rm peak}\gtrsim4\times10^{44}$ erg s$^{-1}$ over rest-frame 1500-4230 Å, placing it within the luminosity range of typical SLSNe-I. SN 2025wny exhibits several unusual features, including a continuum excess and sharp spectral features in the FUV from +20-60 d that coincide with an FUV light-curve plateau and higher inferred blackbody temperatures. SN 2025wny's spectra also show little to no UV line blanketing, no obvious O II absorption despite high temperatures, and evidence for C II, H$α$, and possible He I. Light-curve modeling suggests that SN 2025wny may require a hybrid or non-standard power source. This work provides some of the first detailed constraints on high-redshift SLSNe and establishes SN 2025wny as an essential spectral and photometric reference for identifying and interpreting high-redshift SLSNe discovered by Rubin and Roman.

astro-ph.CO↗

arXiv2026

Follow-up of SN 2025wny III: Spectroscopic Time-delay Measurements of a Strongly Gravitationally Lensed Superluminous Supernova

We present spatially resolved spectra and infer the time-delays between the multiple images of the strongly gravitationally lensed superluminous supernova (SLSN) 2025wny at z=2.015. SN 2025wny is the first known spatially resolved strongly lensed SLSN and provides a unique opportunity to measure lensing delays through the temporal evolution of supernova spectra. We present a spectroscopic dataset spanning several months, including spatially resolved spectra of images A, B, C, D, and E. We identify and measure the wavelength evolution of spectral features using Gaussian-process modeling. The time delays are inferred by jointly fitting the temporal evolution of the spectral features, yielding $Δt_{AB}=-10.3 \pm 2.3$, $Δt_{AC}=0.1 \pm 3.6$, $Δt_{AD}=-65.7 \pm 3.5$, and $Δt_{AE}=3.7 \pm 8.8$ days (68% confidence intervals). These are the among most precise time-delay measurements obtained for a lensed supernova to date, whether from spectroscopic or photometric methods. The longest delay ($Δt_{AD}$) is particularly well constrained, with a ~5% precision. Combined with the lens model presented by Mörtsell et al. (2026), the spectroscopic time-delays give a Hubble constant $H_0 = 70.2^{+8.2}_{-6.1}$ km/s/Mpc. Our analysis demonstrates that spectroscopic evolution provides an independent and complementary route to time-delay measurements in lensed supernova systems, avoiding reliance on photometric light curves alone. As future surveys discover larger samples of lensed supernovae, spectroscopic time-delay measurements will provide an important avenue for precision cosmography.

astro-ph.CO↗

arXiv2026

When Stars Mimic Monsters: Spectral Evidence for an $η$ Carinae-like Giant Eruption in SBS 0335$-$052 E

SBS 0335$-$052 E is an extremely low-metallicity ($Z\sim0.04\,Z_{\odot}$) blue compact dwarf galaxy. An active galactic nucleus has been proposed to explain the broad H$α$ emission and near-infrared (NIR) time variability in super star clusters 1 and 2 (SSCs 1&2). However, Peng et al. discovered broad wings in the forbidden [O III] $\lambda5007$ emission (up to $\sim5\,000\,\rm{km\,s^{-1}}$), challenging the broad-line region interpretation. We present new KCWI/KCRM integral-field spectroscopy to directly compare spectra across multiple SSCs. The nebula surrounding SSCs 1&2 shows unique features. The Ly$β$-pumped O I $\lambda8446$ emission constrains $τ_{\rm\,Lyα}\sim10^8$. Multiple ionization states of iron are detected from Fe$^{+}$ to Fe$^{+4}$. Stellar photoionization models can reproduce the [Fe III]/[Fe II] and [Fe IV]/[Fe III] line ratios at high density ($n_e\sim10^6\,\rm{cm^{-3}}$), but they fail to account for most of the [Fe V] emission. The broad H$α$ wings exhibit an exponential profile; the asymmetric wings extend from $\sim-5\,000\,\rm{km\,s^{-1}}$ to $\sim10\,000\,\rm{km\,s^{-1}}$. Thomson scattering in a radially expanding medium provides a good fit with $v_w\sim200\,\rm{km\,s^{-1}}$, optical depth $τ_e\sim10$, and an outer to inner radius of 10. Enhanced N/O and potentially depleted Fe/O ratios are consistent with CNO-cycled ejecta from massive stars and with dust formation, respectively. We propose that mass loss from a massive star interacting with its circumstellar medium drives a shock that powers the NIR variability, the luminous X-ray point source, and the [Fe V] emission. If confirmed, the proposed stellar eruption would be a distant example of an $η$ Carinae-like giant eruption, and the first in an ultra-low metallicity environment.

astro-ph.GA↗

arXiv2026

Joint Optical and Infrared Observations of N and O Reveal the Dust-Obscured Gas in Haro 3

Accurate chemical compositions of star-forming regions are a critical diagnostic tool to characterize the star formation history and gas flows which regulate galaxy formation. However, the abundance discrepancy factor (ADF) between measurements from the "direct" optical electron temperature ($T_e$) method and from the recombination lines (RL) represents $\sim0.2$ dex systematic uncertainty in oxygen abundance. The degree of uncertainty for other elements is unknown. We conduct a comprehensive analysis of O$^{++}$ and N$^+$ ion abundances using optical and far-infrared spectra of a star-forming region within the nearby dwarf galaxy Haro 3, which exhibits a typical ADF. Assuming homogeneous conditions, the far-IR emission indicates an O abundance which is higher than the $T_e$ method and consistent with the RL value, as would be expected from temperature fluctuations, whereas the far-IR N abundance is too large to be explained by temperature fluctuations. A two-phase analytical model reveals that differential dust obscuration associated with temperature inhomogeneity is likely required to explain all the emission line ratios, and that the total oxygen metallicity of two phases is consistent with the RL metallicity. Our findings underscore the critical importance of resolving the cause of abundance discrepancies and understanding the biases between different metallicity methods. This work represents a promising methodology, and we identify further approaches to address the current dominant uncertainties.

astro-ph.GA↗

arXiv2026

A precessing jet from an active galactic nucleus drives gas outflow from a disk galaxy

To reproduce observed galaxy properties, cosmological simulations require that massive galaxies experience feedback from active galactic nuclei, which regulates star formation within those galaxies. However, the energetics and timescales of these feedback processes are poorly constrained. We combine optical, infrared, sub-millimeter and radio observations of the active galaxy VV 340a, hosting a low-power jet launched from a supermassive black hole at its center. We find that the jet undergoes precession, with a period of (8.2 $\pm~$5.5) $\times~$10$^5$ years, and drives an outflow of gas at a rate of 19.4 $\pm~$7.9 solar masses per year. The jet shocks the gas, producing highly ionized plasma extending several kiloparsecs from the nucleus. The outflow ejects sufficient gas from the galaxy to influence its star formation rate.

astro-ph.GA↗

arXiv2025

Mapping the z ~ 2 Circumgalactic Medium using KBSS Galaxy Pairs

We present new results on the spatial structure and kinematics of the circumgalactic medium (CGM) of z ~ 2 star-forming galaxies drawn from the Keck Baryonic Structure Survey, using Lya and metallic ion absorption recorded in spectra of background galaxies whose sightlines are projected within ~ 30" (physical distances D_tran < 250 kpc) of the foreground galaxy. The sample of 1033 foreground galaxies ( = 2.03; 8 < log(M_star/M_sun) < 11) is probed by the spectra of 736 background galaxies obtained using Keck/KCWI (R ~ 1800) and Keck/LRIS (R ~ 1200). Using the galaxy pair ensemble, we present measurements of absorption strength (W_lambda) and line-of-sight velocity dispersion (sigma) as a function of D_tran, which together with "down-the-barrel" spectra of the foreground galaxies provide unprecedented maps of neutral hydrogen and ionized metals throughout the CGM of star-forming galaxies at "cosmic noon". A 2D map of Lya absorption depth (vs. line-of-sight velocity and D_tran) for the full ensemble shows a distinct transition near D_tran ~ 80 kpc (close to the virial radius of the average foreground galaxy) where the line-of-sight velocity dispersion reaches a minimum and beyond which the Lya absorption depth flattens. Splitting the sample into subsets based on foreground galaxy properties, we find a strong and monotonic correlation of both W_lambda(C IV) and sigma(C IV) with stellar mass (M_star) at all D_tran including DTB (i.e., D_tran ~ 0 - 250 kpc). Taken together, our results suggest that the kinematics, covering fraction, and spatial extent of CGM gas traced by Lya and (especially) CIV are modulated primarily by halo mass, and that a significant fraction of the CGM gas may be unbound.

astro-ph.GA↗

arXiv2025

Shockingly Effective: Cluster Winds as Engines of Feedback in Starburst Galaxy VV 114

We present high-resolution Keck Cosmic Web Imager (KCWI) and MUSE IFU spectroscopy of VV 114, a local infrared-luminous merger undergoing a vigorous starburst and showing evidence of galactic-scale feedback. The high-resolution data allow for spectral deblending of the optical emission lines and reveal a broad emission line component ($σ_{\rm{broad}} \sim$~100--300 km s$^{-1}$) with line ratios and kinematics consistent with a mixture of ionization by stars and radiative shocks. The shock fraction (percent ionization due to shocks) in the high velocity gas is anticorrelated with projected surface number density of resolved star clusters, and we find radial density profiles around clusters are well fit by models of adiabatically expanding cluster winds driven by massive stellar winds and supernovae (SNe). The total kinetic power estimated from the cluster wind models matches the wind+SNe mechanical energy deposition rate estimated from the soft band X-ray luminosity, indicating that at least 70\% of the shock luminosity in the galaxy is driven by the star clusters. \emph{Hubble Space Telescope} narrow band near-infrared imaging reveals embedded shocks in the dust-buried infrared nucleus of VV 114E. Most of the shocked gas is blueshifted with respect to the quiescent medium, and there is a close spatial correspondence between the shock map and the \emph{Chandra} soft band X-ray image, implying the presence of a galactic superwind. The energy budget of the superwind is in close agreement with the total kinetic power of the cluster winds, confirming the superwind is driven by the starburst.

astro-ph.GA↗

arXiv2025

The BTSbot-nearby discovery of SN 2024jlf: rapid, autonomous follow-up probes interaction in an 18.5 Mpc Type IIP supernova

We present observations of the Type IIP supernova (SN) 2024jlf, including spectroscopy beginning just 0.7 days ($\sim$17 hours) after first light. Rapid follow-up was enabled by the new $\texttt{BTSbot-nearby}$ program, which involves autonomously triggering target-of-opportunity requests for new transients in Zwicky Transient Facility data that are coincident with nearby ($D<60$ Mpc) galaxies and identified by the $\texttt{BTSbot}$ machine learning model. Early photometry and non-detections shortly prior to first light show that SN 2024jlf initially brightened by $>$4 mag/day, quicker than $\sim$90% of Type II SNe. Early spectra reveal weak flash ionization features: narrow, short-lived ($1.3 < τ~\mathrm{[d]} < 1.8$) emission lines of H$α$, He II, and C IV. Assuming a wind velocity of $v_w=50$ km s$^{-1}$, these properties indicate that the red supergiant progenitor exhibited enhanced mass-loss in the last year before explosion. We constrain the mass-loss rate to $10^{-4} < \dot{M}~\mathrm{[M_\odot~yr^{-1}]} < 10^{-3}$ by matching observations to model grids from two independent radiative hydrodynamics codes. $\texttt{BTSbot-nearby}$ automation minimizes spectroscopic follow-up latency, enabling the observation of ephemeral early-time phenomena exhibited by transients.

astro-ph.HE↗

arXiv2024

Expansion properties of the young supernova type Iax remnant Pa 30 revealed

The recently discovered Pa 30 nebula, the putative type Iax supernova remnant associated with the historical supernova of 1181 AD, shows puzzling characteristics that make it unique among known supernova remnants. In particular, Pa 30 exhibits a complex morphology, with a unique radial and filamentary structure, and it hosts a hot stellar remnant at its center, which displays oxygen-dominated, ultra-fast winds. Because of the surviving stellar remnant and the lack of hydrogen and helium in its filaments, it has been suggested that Pa 30 is the product of a failed thermonuclear explosion in a near- or super-Chandrasekhar white dwarf, which created a sub-luminous transient, a rare sub-type of the Ia class of supernovae called type Iax. We here present a detailed study of the 3D structure and velocities of a full radial section of the remnant. The Integral Field Unit (IFU) observations, obtained with the new red channel of the Keck Cosmic Web Imager spectrograph, reveal that the ejecta are consistent with being ballistic, with velocities close to the free-expansion velocity. Additionally, we detect a large cavity inside the supernova remnant and a sharp inner edge to the filamentary structure, which coincides with the outer edge of a bright ring detected in infrared images. Finally, we detect a strong asymmetry in the amount of ejecta along the line of sight, which might hint to an asymmetric explosion. Our analysis provides strong confirmation that the explosion originated from SN 1181.

astro-ph.SR↗

arXiv2024

KBSS-InCLOSE I: Design and First Results from the Inner CGM of QSO Line Of Sight Emitting Galaxies at z~2-3

We present the design and first results of the Inner Circumgalactic Medium (CGM) of QSO Line of Sight Emitting galaxies at $z\sim 2-3$, KBSS-InCLOSE. The survey will connect galaxy properties (e.g., stellar mass $M_*$, interstellar medium ISM metallicity) with the physical conditions of the inner CGM (e.g., kinematics, metallicity) to directly observe the galaxy-scale baryon cycle. We obtain deep Keck/KCWI optical IFU pointings of Keck Baryonic Structure Survey (KBSS) QSOs to discover new star-forming galaxies at small projected distances $b\lesssim12"$ (98 kpc, $\overline{z}=2.3$), then obtain follow-up Keck/MOSFIRE NIR spectra to confirm their redshifts. We leverage KBSS images and Keck/HIRES QSO spectra to model stellar populations and inner CGM absorption. In this paper, we analyze two QSO fields and discover more than 15 new galaxies with KCWI, then use MOSFIRE for two galaxies Q2343-G1 ($z=2.43$; G1) and Q2233-N1 ($z=3.15$; N1), which are both associated with Damped Lyman Alpha absorbers. We find that G1 has typical $M_*$,UV/optical emission properties. N1 has lower $M_*$ with very strong nebular emission. We jointly analyze neutral phase CGM and ionized ISM in N/O (for the first time at this $z$), dust extinction, and high-ionization CGM finding that: G1's CGM is metal poor and less evolved than its ISM, while N1's CGM and ISM abundances are comparable; their CGM shows $\sim1$ dex less dust extinction than the ISM; and G1's CGM has direct evidence of hot, metal-rich galactic outflow ejecta. These findings support that metals and dust are driven into the CGM from outflows, but may also be e.g., stripped ISM gas or satellite enrichment. The full KBSS-InCLOSE sample will explore these scenarios.

astro-ph.GA↗

arXiv2024

SN 2023zaw: an ultra-stripped, nickel-poor supernova from a low-mass progenitor

We present SN 2023zaw $-$ a sub-luminous ($\mathrm{M_r} = -16.7$ mag) and rapidly-evolving supernova ($\mathrm{t_{1/2,r}} = 4.9$ days), with the lowest nickel mass ($\approx0.002$ $\mathrm{M_\odot}$) measured among all stripped-envelope supernovae discovered to date. The photospheric spectra are dominated by broad He I and Ca NIR emission lines with velocities of $\sim10\ 000 - 12\ 000$ $\mathrm{km\ s^{-1}}$. The late-time spectra show prominent narrow He I emission lines at $\sim$1000$\ \mathrm{km\ s^{-1}}$, indicative of interaction with He-rich circumstellar material. SN 2023zaw is located in the spiral arm of a star-forming galaxy. We perform radiation-hydrodynamical and analytical modeling of the lightcurve by fitting with a combination of shock-cooling emission and nickel decay. The progenitor has a best-fit envelope mass of $\approx0.2$ $\mathrm{M_\odot}$ and an envelope radius of $\approx50$ $\mathrm{R_\odot}$. The extremely low nickel mass and low ejecta mass ($\approx0.5$ $\mathrm{M_\odot}$) suggest an ultra-stripped SN, which originates from a mass-losing low mass He-star (ZAMS mass $<$ 10 $\mathrm{M_\odot}$) in a close binary system. This is a channel to form double neutron star systems, whose merger is detectable with LIGO. SN 2023zaw underscores the existence of a previously undiscovered population of extremely low nickel mass ($< 0.005$ $\mathrm{M_\odot}$) stripped-envelope supernovae, which can be explored with deep and high-cadence transient surveys.

astro-ph.HE↗

arXiv2024

Metals in Star-Forming Galaxies with KCWI. I. Methodology and First Results on the Abundances of Iron, Magnesium, and Oxygen

Understanding the chemical enrichment of different elements is crucial to gaining a complete picture of galaxy chemical evolution. In this study, we present a new sample of 46 low-redshift, low-mass star-forming galaxies at $M_*\sim 10^{8-10}M_{\odot}$ along with two quiescent galaxies at $M_*\sim 10^{8.8}M_{\odot}$ observed with the Keck Cosmic Web Imager (KCWI), aiming to investigate the chemical evolution of galaxies in the transition zone between Local Group satellites and massive field galaxies. We develop a novel method to simultaneously determine stellar abundances of iron and magnesium in star-forming galaxies. With the gas-phase oxygen abundance (O/H)$_{\rm g}$ measured using the strong line method, we are able to make the first-ever apples-to-apples comparison of $α$ elements in the stars and the ISM. We find that the [Mg/H]$_*$-[O/H]$_{\rm g}$ relation is much tighter than the [Fe/H]$_*$-[O/H]$_{\rm g}$ relation, which can be explained by the similar production processes of $α$ elements. Most galaxies in our sample exhibit higher [O/H]$_{\rm g}$ than [Fe/H]$_*$ and [Mg/H]$_*$. In addition, we construct mass-metallicity relations (MZRs) measured as three different elements (Fe$_*$, Mg$_*$, O$_{\rm g}$). Compared to the gas O-MZR, the stellar Fe- and Mg-MZRs show larger scatter driven by variations in specific star formation rates (sSFR), with star-forming galaxies exhibiting higher sSFR and lower stellar abundances at fixed mass. The excess of [O/H]$_{\rm g}$ compared to stellar abundances as well as the anti-correlation between sSFR and stellar abundance suggests that galaxy quenching of intermediate-mass galaxies at $M_*\sim 10^{8-10}M_{\odot}$ is primarily driven by starvation.

astro-ph.GA↗

arXiv2021

Connecting Galactic Outflows and Star Formation: Inferences from H-alpha Maps and Absorption Line Spectroscopy at 1 < z < 1.5

We investigate the connection between galactic outflows and star formation using two independent data sets covering a sample of 22 galaxies between $1 \lesssim z \lesssim 1.5$. The HST WFC3/G141 grism provides low spectral resolution, high spatial resolution spectroscopy yielding H$α$ emission line maps from which we measure the spatial extent and strength of star formation. In the rest-frame near-UV, Keck/DEIMOS observes Fe II and Mg II interstellar absorption lines, which provide constraints on the intensity and velocity of the outflows. We compare outflow properties from individual and composite spectra with the star formation rate (SFR) and SFR surface density (SigmaSFR), as well as the stellar mass and specific star formation rate (sSFR). The Fe II and Mg II equivalent widths (EWs) increase with both SFR and SigmaSFR at $\gtrsim 3σ$ significance, while the composite spectra show larger Fe II EWs and outflow velocities in galaxies with higher SFR, SigmaSFR, and sSFR. Absorption line profiles of the composite spectra further indicate that the differences between subsamples are driven by outflows rather than the ISM. While these results are consistent with those of previous studies, the use of H$α$ images makes them the most direct test of the relationship between star formation and outflows at $z>1$ to date. Future facilities such as the James Webb Space Telescope and the upcoming Extremely Large Telescopes will extend these direct, H$α$-based studies to lower masses and star formation rates, probing galactic feedback across orders of magnitude in galaxy properties and augmenting the correlations we find here.

astro-ph.GA↗